Early Mesozoic burst of morphological disparity in the slow-evolving coelacanth fish lineage

Since the split of the coelacanth lineage from other osteichthyans 420 million years ago, the morphological disparity of this clade has remained remarkably stable. Only few outliers with peculiar body shape stood out over the evolutionary history, but they were phylogenetically and stratigraphically independent of each other. Here, we report the discovery of a new clade of ancient latimeriid coelacanths representing a small flock of species present in the Western Tethys between 242 and 241 million years ago. Among the four species, two show highly derived anatomy. A new genus shows reversal to plesiomorphic conditions in its skull and caudal fin organisation. The new genus and its sister Foreyia have anatomical modules that moved from the general coelacanth Bauplau either in the same direction or in opposite direction that affect proportions of the body, opercle and fins. Comparisons with extant genetic models shows that changes of the regulatory network of the Hedgehog signal gene family may account for most of the altered anatomy. This unexpected, short and confined new clade represents the only known example of a burst of morphological disparity over the long history of coelacanths at a recovery period after the Permian–Triassic Mass Extinction.


General morphology
Rieppelia is a medium size coelacanth than can reach an estimated total body length of about Rieppelia is a distinctively short coelacanth. The length of the head (without the enlarged opercle), the trunk and the caudal fin each represent one third of the total body length, giving Rieppelia a plump appearance shared with Foreyia 1 .

Dermal bones of the skull roof
Dermal bones of the skull roof of Rieppelia are well known in several specimens visible in external and internal views. The skull roof is almost as long as broad forming in dorsal view a hexagon with edges of regular size, the anterior and posterior edges being slightly shorter than the lateral edges.
As in all coelacanths, the skull of Rieppelia is divided into two parts, namely the parietonasal shield and the postparietal shield, which are generally delimited by an intracranial joint. All the bones making up the skull roof -except the snout bones -are tightly sutured to one another.
Parietonasal and postparietal shields are always preserved in close contact, even if the rest of the skeleton is lacking (e.g. PIMUZ T 5903) or was disturbed postmortem (e.g. PIMUZ T 1321).
The two shields appear to be always tightly attached one another (Figs 2, S1a-b, S2), displaying a gap at the level of the supraorbitals and supratemporals ( Fig. S3a- Moreover, in ventral view the surface of the posterior parietals appears to be reduced in dorsal view, which is consistent with the fact that the posterior parietals overlap the postparietals. The intracranial joint (i.j) appears to be almost straight with some few indentations in dorsal view (Figs 2, S3) while it is completely straight in ventral view (Fig. S1). Therefore both shields were strongly sutured together (character 1) and the intracranial joint was not functionnal. This derived character shared with Foreyia 1 is unique among coelacanths.
The skull roof of Rieppelia departs from the standard morphology of latimerioids coelacanths by its parietonasal shield being approximatively the same length than the postparietal shield (Figs 2, S1a-b, S2, S3a-b) (character 2), a feature commonly found in Palaeozoic coelacanths.

Parietonasal shield
Beside the unusual morphology of some dermal bones, the skull roof pattern of Rieppelia is characteristic of coelacanths (Figs 2, S2, S3).
The snout bones have matching contours ( Fig. S1a-b) and are independent from one another (character 3) although they are somewhat attached to one another (Fig. S2).
Each premaxilla (Pmx) is rectangular and carries a well-developed dorsal lamina  fig. 3.1). Therefore, this bone is identified as a rostral ossicle and the large opening as the anterior opening for the rostral organ (a.ros), which is then contained within separated rostral ossicles (character 6).
Lateral to the premaxilla is the lateral rostrals (L.r) (Figs S1a-b, S2). Usually, the shape of the lateral rostral in actinistians is relatively constant 3 and is composed of an elongated narrow tubular portion and an anterior part more developed that contacts the tectals on its dorsal margin, and has a more or less developed ventral process. The shape of the lateral rostral of Rieppelia, however, is unique among actinistians because its height is greater than its length. The dorsal region of the lateral rostral is overdeveloped and separate the unique tectal from the supraorbital series (Figs S1a-b, S2), while normally the tectal-supraorbital series is uninterrupted in coelacanths. Based on this bone pattern, it is assumed that the lateral rostral had fused with the neighbouring tectal, which results in the hypertrophied aspect of the lateral rostral. The ventral process of the lateral rostral is poorly developed (Fig. S2), as for instance in Rhabdoderma 3 . In internal view, the anterior tubular portion displays a small excavation opening on the ventral margin of the bone, which may correspond to the mark of the anterior nostril (nos.a) (Fig. 3).
In this area, the anterior tubular portion is curved (Fig. S2) reinforcing the hypothesis that the nostril opens at this location. At the posterodorsal margin of the tubular portion and at the junction of the preorbital and lachrymojugal is an opening interpreted as the posterior nostril (nos.p) (Figs S1a-b, S2).
In front of the anterior parietal and wedged between the nasal and the lateral rostral is a single rectangular tectal (Te). This bone is smaller than the nasal and as large as the rostral ossicles.
It is identified as a tectal because it lies at a level anterior to the parietal and is adjacent to the triple junction of the sensory canal ( Fig. S1a-b) as in Latimeria 3 . As mentioned above, this unique tectal is separated from the supraorbital series by the lateral rostral. It is supposed that the tectal that usually connects other tectals to the supraorbital series in coelacanths has been either lost or, more likely, incorporated into the dorsal portion of the lateral rostral. Indeed, the tectals seem to fuse with the neighbouring bones, namely the nasal or lateral rostral (Fig. S2). Whiteia 3 ). Miguashaia is the only other actinistians that has a condition different from the usual condition observed in actinistians. In it, the posterior most supraorbital directly contacts the intertemporal which is, as the supratemporal, a bone of the lateral series of the postparietal shield. In Rieppelia, the anterior supraorbital is the longest bones of the lateral series and the second supraorbital is as long as, or slightly longer than the posterior most supraorbital. The anterior and posterior supraorbitals are rectangular, while the second supraorbital is squarish.
The third posterior supraorbital expends ventrally in such a way that its anteroventral margin participates to the posterodorsal coutour of the orbit. When regarded in anterior view, all supraorbitals are strongly angled in their middle, forming a sharp angle between the skull roof and cheek. This angle marks a strong crest running throughout the middle of the supraorbitals series and crossing longitudinally the upper part of the opercle (Fig. S2a). In internal view, the posterior third supraorbital presents in the center of its posterior margin a ridged surface that corresponds to the insertion point for the opercular ligament (op.lig) (Figs 3, S1a-b). Along the internal margin forming the orbit, all three supraorbitals are reinforced with a thickening of the ossification marked with curved grooves parallel to the orbital margin (Figs 3, S1a-b). On the posterior third supraorbital, this thick bony portion is more reduced than on the other two supraorbitals. This reinforced structure is also present on the postorbital-squamosal bone and the preorbital, but is absent from the lachrymojugal. The function of this structure is not clear but it may correspond to a reinforcement of the orbital region. Sclerotic ossicles have not been observed in any available specimens, and it is then assumed that a sclerotic ring is absent (character 56).
The preorbital (Preo) (character 13) is round to ovoid in shape, and is sutured with the anterior supraorbital, the lachrymojugal and the lateral rostral (Figs 3, S1a-b, S2). In internal view, the orbital margin of the preorbital presents the same overdeveloped bony structure than observed on the supraorbitals (Figs 3, S1a-b). The anteroventral edge of the preorbital is notched for the exit of the posterior nostril (nos.p). Therefore, this notch should not be regarded as the corresponding notch observed on the mid-length of the ventral margin of the preorbital of Foreyia interpreted as the posterior opening of the rostral organ 3 . Consequently, the preorbital of Rieppelia is not pierced or notched for the posterior openings of the rostral organ unlike all other actinistians having a preorbital. As the cheek is well ossified and completely known, the posterior openings of the rostral organ (p.ros) supposedly opened in the anterior part of the orbital space (characters 46 and 47), in a position similar to that of Latimeria. It is excluded that the pore opening on the lachrymojugal (Figs 2, S3a-b) is the exit of the posterior opening of the rostral organ because in a large specimen (PIMUZ T 4985), this opening is an elongated pore running from the center of the bone to its posterior margin, a position incompatible with interpreting this pore as posterior opening of the rostral organ. Furthermore, after reconstruction, it seems that the parasphenoid is placed above this opening, thus excluding the identification of this pore as the posterior openings of the rostral organ, which should be located dorsal to this bone for anatomical reason.
Posteriorly to the rostral ossicles and tectals lies a pair of small squarish to rectangular nasals (Na) (Figs 2, S1a-b, S2). The nasals are slightly larger than the rostral ossicles but are considerably smaller than the parietals. The pair of nasals is sometimes separated by an internasal (Ina), strongly sutured with the neighbouring nasal (Fig. S2). The presence of this bone, however is not constant among the available specimens ( Fig. S1a-b) (character 7).
Rieppelia has two pairs of parietals (Pa) (character 8). The parietals are square to rectangular, and they are approximatively of the same length (character 9), but the total surface of the anterior parietal is smaller than the one of the posterior parietal. The two pairs of parietals are then of similar size, as in Ticinepomis 4 and Foreyia 1 , but unlike in the Latimeriinae. The sutural pattern between the anterior and posterior parietals is straight (Figs 2, S3a-b), resembling to the intracranial joint condition, or very slightly interdigitated (Fig. S2). In internal view, the anterior parietals appear longer than the posterior parietals (

Postparietal shield
The postparietals (Pp) of Rieppelia are almost rectangular, being slightly longer than wide (Figs 2, S1a-b, S2, S3a-b). Thus, the postparietal is, as in Allenypterus, relatively equidimensional, which is considered by Forey 3 as an unusual feature in coelacanths. The lateral border is slightly curved in its posterior half in order to receive the supratemporal bone.
Usually in coelacanths, the postparietal contacts the postorbital. However, in Rieppelia, the postparietal is not in contact with the postorbital-squamosal bone because it is separated by the posterior most supraorbital. This characteristic is possibly shared with Foreyia 1 in which all bones of the postparietal shield are fused together, and it is only observed in some few Palaeozoic actinistians, such as Miguashaia, Gavinia and potentially Coelacanthus granulatus.
Apart of the supratemporal, there is no other canal-bearing bone, namely an intertemporal, along the postparietal (character 14).
Each postparietal is flanked by a smaller rectangular to ovoidal supratemporal (Stt) (Figs 2, S1a-b, S2, S3a-b). The supratemporal is in direct contact -but is not sutured -with the posterior third supraorbital, being separated by the intracranial joint. Therefore, the anterior margin of the supratemporal is not separated from the parietonasal shield by the postparietal bone, which is a condition unique among actinistians. The posterior margin of the supratemporal is rounded, fitting the concave anterior margin of the lateral extrascapular. The supratemporal bears a welldeveloped long and thin descending process (v.pr.Stt) (character 16) (Fig. 3).
The posterior margin of the supratemporal and the postparietal are at the same level resulting in a straight posterior margin of the skull roof (character 17) (Figs 2, S1a-b, S2, S3a-b), a characteristic commonly observed in Palaeozoic coelacanths such as Allenypterus 3 , The extrascapular series is represented by three large bones, one median (Ext.m) and a lateral (Ext.l) one on each side (characters 20 and 21) (Figs 2, S1a-b, S2, S3a-b). The lateral extrascapulars are almost square and equidimensional while the median extrascapular is slightly less wide, being then more rectangular to ovoidal. This configuration of three more or less large extrascapulars lying posteriorly to the supratemporals and postparietals is reminiscent of Palaeozoic coelacanths, for instance Miguashaia 6 , Diplocercides 5 , Allenypterus and  The bone is almost equidimensional and its length is only slightly greater than its width, giving to the lachrymojugal an appearance of a relatively short and thick bone with a roughly triangular shape (character 43). This shape is reminiscent of the lachrymojugal of Foreyia (the lachrymojugal+squamosal in 1 ) and, to a lesser extent, of presence of a subopercle, which has never been observed in the available specimens, and consequently regarded as absent (character 41). Moreover, as the opercle of Rieppelia covers the area normally occupied by the opercle and subopercle in other coelacanths, a fusion of these two bones cannot be excluded during ontogenesis in the genus. Interestingly, the preopercle of the juvenile/newborn specimen (Fig. 3), which is visible in internal aspect, present a strong mark/groove in its first anterior third. The latter may be interpreted as a suture between two bones, a feature that has never been observed in external view on available specimens. As this feature is observed in a specimen regarded as a juvenile/newborn specimen, this suture may correspond to a remnant suture of an earlier ontogenic stage. Before the synthetic work of

Lower jaw
The bones of the lower jaw of Rieppelia are never preserved articulated among the available specimens (Figs S1a-b, S2), except to some extent, in the holotype ( Fig. 2a-b) and the juvenile/newborn specimen (Fig. 3). When reconstructed (Figs 2c, S8), the lower jaw is small but with an organization comparable to that of other coelacanths.
The articular facets have not been observed on any specimens and it is then not possible to assess if the retroarticular and articular are co-ossified or not (character 57).
The angular (Ang) is the largest bone of the mandible (Figs 2, 3, S1a-b). The angular is parallel-sided in the same way as in Ticinepomis spp. 4,7,8 . Its ventral margin is very slightly concave. The deepest point is located approximately midway along the length of the angular.
The prearticular (Part) is a large bone, which has its mesial surface covered by round to ovoid sockets that accommodated teeth ( Fig. S1a-b).
In the juvenile/newborn specimen only, the splenial (Spl) and the dentary are observed in articulation (Fig. 3). The splenial appears to be deep with parallel margin and is as long as the dentary as in Ticinepomis spp. 4,7,8 and Foreyia 1 . The ventral margin of the splenial is very slightly concave but together with the angular, the ventral margin of the lower jaw appears to be very curved. The anteroventral portion of the splenial is slightly curved downward, similarly, in the same way, but however less than in Ticinepomis spp. 4,7,8 , Foreyia 1 , Dobrogeria 9 and Whiteia woodwardi ( 3 , figs 5.9a and 5.9c).
The dentary (De) is only observed in the juvenile/newborn specimen (Fig. 3). It forms a long process with a straight oral border extending posteriorly as in Ticinepomis spp. 4,8 and Foreyia 1 .
In its mid part, the dentary appears to be as wide as the splenial and becomes slightly narrower anteriorly. The posterior margin of the dentary forms a small hook but unfortunately the exact relationship between the dentary and the angular is not clear, preventing confirmation that the dentary is hook-shaped (character 58). It is also impossible to determine the condition of the lateral swelling on the dentary (character 59) but this feature is probably absent when the general shape of the mandible is considered.
The dentition of Rieppelia is very distinctive among coelacanths. In the holotype (Figs 2a-b, S5a) and juvenile/newborn specimens (Fig. 3), rows of teeth are observed directly above the oral margin of the bones of the lower jaw. All teeth are curved and measure between 1 mm to 1.3 mm long and are found separate from the dentary (character 60). Although all teeth are of the same size, few are gathered by clusters of three curved teeth forming small toothed elements, whereas the majority lies in pack but appears to be free, independent to each other. It is excluded that these teeth belong to the basibranchial apparatus as they are always observed in the oral area of the jaws in many specimens (Figs 2a-b, 3, S1, S2, S3a-b).
The free teeth are considered to be shedded teeth of the dentary tooth plates (t.p.d) that were borne by the dentary (Fig. 2a-b). They probably laid free in the skin as in Latimeria, which is considered to be a derived condition 3  in Ticinepomis peyeri that has coronoids and dermopalatines sharing the same structure and shape of teeth 4 . As there is no size variation between the coronoids, the coronoid opposite to the posterior end of the dentary is considered to be not modified (character 63). The teeth are pointed and smooth (character 65), and are identified as fangs (character 64). The coronoid structure of Rieppelia is thus different from the one of Latimeria that is composed of a dental plate on which rests a large fang, one mid-sized caniniform tooth and numerous small roundshaped teeth 12 .
In the juvenile/newborn specimen, a fragmented and ill-defined bone located above the right angular is interpreted with caution as the principal coronoid (p.Co) (Fig. 3). This bone has shifted from its original position meaning that it was separated from the angular (character 61).
Only one clearly identifiable gular plate (Gu) visible in external view has been observed

Sensory canals, cranial nerves and pit lines
In Rieppelia, the strong ornamentation of its dermal bones makes difficult to detect the opening of the sensory canals but a careful observation indicates that they are present on the bones of the skull roof, the cheek and the lower jaw. The specimens preserved in internal view display grooves on the internal surface of the bones that are interpreted, depending of their location, as the path of the cranial nerves or as the sensory canals. These structures may also be observed in volume but representing the filling of the underlying canals that have been removed (i.e. for instance part and counterpart). In some part, especially in the snout, these structures seem to represent the sensory canal together with the path of the cranial nerves, which have been compressed together during fossilization. Indeed, regarding the disposition of the sensory pores and the observed grooves, it appears that, in the snout area, the sensory canals may have been located just above the nerves. Such a situation would not be surprising as in the living Latimeria the nerves and the sensory canals are located one above the other or close to each other 10,14 . In the middle part of the skull roof, namely on the parietals and postparietals, the sensory canals are placed laterally to the path of the groove, here representing the path of the nerve. In this part the nerve sends branches to innervate the supraorbital sensory canal. The situation of the nerves in the posterior part, the cheek and the lower jaw remains unknown.

Sensory canals
Generally, the pores for the sensory canals are hard to detect because of the strong ornamentation of the dermal bones and especially because it is difficult to distinguish a true pore from the sockets of lost a lost ornament. On the skull roof, the pores of the sensory canal are numerous and small on the snout and become rarer and smaller posteriorly, being absent on the extrascapular series (Fig. S2). Therefore, the ethmosphenoid portion of Rieppelia must have been a more sensitive region than the otico-occipital portion.
On the snout, most pores of the supraorbital sensory canal (p.so.s.c) opens at the sutural contact between ossifications, but some pores are located within the bones, namely on the tectal and the premaxillae (Fig. S2).  fig. 21). Therefore, compared to Latimeria, it seems that Rieppelia has one more neuromast innervating the supraorbital canal.
There are few openings for the otic sensory canal (p.ot.s.c) ( Fig. S3a-b). At the margin of the supratemporal and the postparietal, there is a small pore formed by two neighbouring notches.
Few round pores are located in the middle of the supratemporal indicating that the otic sensory canal runs through the center of the bone, as in other coelacanths. At the posterior margin of the supratemporal is a notch (Fig. S3a-b) or a pore (Fig. S2). On the surface of the postparietal, there is no pore for the median branch of the otic canal (character 24) and no anterior branches of supratemporal commissure (character 25).
The extrascapular series is devoid of any pore. However, the supratemporal commissure which is in some specimens surrounded ventrally by much smaller pores, forming a line perpendicular to the ventral margin of the bone ( Fig. S3a-b). The large pore indicates the path of the main infraorbital sensory canal and the small pores represent short secondary branches.
In a large specimen (PIMUZ T 4985), this large pore appears as an elongated pore running from the center of the bone to its posterior margin. Apart the pore(s) observed on the lachrymojugal, the other bones of the cheek show no visible pores. Therefore, the exact pattern of the cheek sensory canals (characters 50 and 51) and the junction between the infraorbital and the jugal sensory canals are unclear. Interestingly, the situation observed on Rieppelia is the opposite of that observed on Foreyia, which has no pore on its lachrymojugal (lachrymojugal+squamosal of 1 ) but has pores on the postorbital 1 .

Otic lateral line nerve
In internal view the bones of the skull roof are crossed by strong grooves that we interpret has the path of the superficial ophthalmic ramus of the anterodorsal lateral line nerve (s.opth) (Figs S1a-b, S5c). This groove can be well observed especially in the specimen PIMUZ T 1638 ( Fig. S1a-b). The groove starts to mark the bone anteriorly to the mid-length of the postparietal.
It suggests that the sensory ganglion of the superficial ophthalmic ramus of the anterodorsal lateral line nerve was probably located in the otico-occipital portion as in Latimeria 14 . The groove exits the postparietal to enter the posterior parietal by crossing the intracranial joint. The groove runs along the mesial side of the parietal descending process and passes across the middle of the center of ossification of the posterior parietal. In the anterior parietal, the groove runs between the lateral margin and the center of ossification of the bone. At midway, the groove appears to diverge medially to form a long groove that passes through the center of ossification. The exact end of this medial groove is not obvious but it gets very close from its antimere. In another specimen, namely PIMUZ T 1755 (Fig. S5c), this medial groove is absent either because of taphonomic reason or because the medial groove observed in PIMUZ T 1638 is not correctly interpreted and is rather a crack. However, the first hypothesis is preferred here because the walls of the medial groove present the same thin bony surface observed in the wall of the main groove, in contradiction with the second hypothesis. Therefore, compared with Latimeria 14,15 , this groove may possibly correspond to the major ramule that innervates the sensory epithelium associated with the two posterior rostral tubes. The location of this groove at the level of the anterior portion of the orbital space also strengthens the hypothesis that the openings for the posterior rostral tubes are located in the anterior part of the orbit, just in front of the eye, as in Latimeria. In PIMUZ T 1755 (part and counterpart), we detected three laterally directed groove (better seen in 3D on the part) at the level of the anterior parietal (Fig. S5c), which seem to correspond to the three foramens observed on the floor of the supraorbital sensory canal of PIMUZ T 5903 ( Fig. S3a-b,d). On PIMUZ T 1638, the foramens are difficult to detect and seem to correspond to enlargements of the groove in which is located a deepening directed towards the inside of the bone, i.e. towards the sensory canal ( Fig. S1a-b). Comparing the localisation of the groove and the openings for the supraorbital sensory canal (Figs S1a-b, S2, S3a-b,d), it appears that the supraorbital sensory canal lies lateral to the groove at the level of the postparietals up to the anterior parietals. In the snout, however, the situation is different and the openings for the supraorbital sensory canal are located directly above or very close to the groove for the nerve. From this perspective both structures may have been merged together during fossilisation making hard to differentiate them. Thus, at the junction between the anterior parietal, the tectal and the lateral rostral, the groove splits into two grooves ( Fig. S1a-b). One groove runs within the lateral rostral and ends lateral to the anterior opening of rostral organ.
The other groove continues through the center of ossification of the tectal and the nasal. At the level of the nasal and rostral ossicles, the groove gets closer medially to its antimere and then finish by forming a loop laterally, which can be clearly observed in PIMUZ T 1755 (Fig. S5c).

Pit lines
Because of the strong ornamentation of the bones, the absence/presence of grooves for pit lines is difficult to assess, but a carful observation shows that none is present on the postparietals

Neurocranium and parasphenoid
The No vomers have been identified in the available specimens (character 81) but their true absence remain questioned here.
The basisphenoid (Bsph) has no basipterygoid process (character 73) (Fig. 3). The condition of the suprapterygoid processes cannot be assessed (character 80). The antotic processes The parasphenoid (Par) is found apart from the basisphenoid (Fig. 3). Unfortunately, because the scattered preservation, it is impossible to know how was the contact between both bones (character 72). However, the position of the processus connectens may suggest that the parasphenoid was probably not meeting the processus connectens. The parasphenoid is a long bone that narrows in its mid-length and expands anteriorly where two parallel ridges marks as small lateral wings (a.w.par) (character 79). As the bone is strongly flattened due to taphonomic processes, it must have been narrower in life. There is no opening in the parasphenoid for the buccohypophysial canal, meaning that it was closed (character 78).
Because the parasphenoid is preserved in dorsal view, its dentition cannot be observed (character 77).
The otico-occipital portion of the braincase is well developed and composed of a separate basioccipital and a pair of prootics (character 75) that surround two catazygal plates (Fig. 3).
Therefore, the otico-occipital portion of Rieppelia presents the derived condition by being ossified as separate elements, unlike plesiomorphic coelacanths having this portion ossified in a single element, as for instance Diplocercides 3 .
The basioccipital (Boc) forms the posterior limit of the basicranial fenestra (Fig. 3). Its posterior margin is partially covered by the cleithrum on the juvenile/newborn specimen (PIMUZ T 3376), but this margin can be indirectly observed. The exact nature of the suture between the basioccipital and the prootic (character 82) is hard to see because most of the sutural contact is hidden by the anocleithrum.
The pair of prootics (Pro) are relatively broad with an approximately triangular shape (Fig. 3).
Their posterior portion, where they suture with the basioccipital, is broad in such a way that they do not form an elongated and thin posterior wing as for instance in Holophagus ( 3 , fig. 6.9).
An anterior and a posterior catazygals (a.Cat; p.Cat) plates occupy the basicranial fenestra ( Fig. 3). Those two plates embraced ventrally the notochord in life. The posterior catazygal has a trapezoidal shape with an anterior margin slightly swollen, and the anterior catazygal is rectangular-shaped. The anterior catazygal is larger than the posterior catazygal, similarly as, for instance, in Whiteia 3 .

Palatoquadrate, hyoid and gill arches 2.7.1 Palatoquadrate
The bones of the suspensorium are rarely preserved in available specimens. These bones seem to be all present in the juvenile/newborn specimen (PIMUZ T 3376) but their identification should be regarded with caution.
The pterygoid (Pt) is probably the best identified bone of the suspensorium. In the juvenile/newborn specimen (PIMUZ T 3376), this bone forms a low and elongated triangle The identification of the metapterygoid is uncertain in the juvenile/newborn specimen (PIMUZ T 3376) as bones of various shapes can be interpreted as such, and we leave the identification unresolved.
In the juvenile/newborn specimen (PIMUZ T 3376), a pair of rectangular bone are interpreted as ectopterygoids (Ecpt) (Fig. 3). One of them visible in mesial aspect presents some rounded teeth similar to that borne on the pterygoid.
Close to the pterygoid are two small triangular bones that are interpreted as the autopalatines (Aut) (Fig. 3). This identification is reinforced because one of them is in direct contact with one of the ectopterygoid.

Branchial arches and urohyal
In the juvenile/newborn specimen (PIMUZ T 3376), one ceratohyal and 8 to 9 ceratobranchials are preserved (Fig. 3). Therefore, there are at least four pairs of ceratobranchials (Cb). One of the supposedly ceratobranchials (Cb?) have a shape recalling an epibranchials. Usually there are five pairs of ceratobranchials in actinistians 3 . Nevertheless, the situation of the branchial apparatus of Rieppelia is reminiscent of the one of Dobrogeria. In this latter, four pairs of broad ceratobranchials, although a fifth was probably present, and two small potential epibranchials are known 9 .
The ceratohyal (Ch) has a small process expending from its central ventral border, giving to the bone the characteristic shape of the ceratohyal of coelacanths 3 (Fig. 3). The central position of this process on the ceratohyal is reminiscent to that of, for instance, Ticinepomis spp. 4 , In the holotype (PIMUZ T 5902), there is large and diamond-shaped bone (Bb?) ( Fig. 2a-b), which recalls the mostly cartilaginous basibranchial of Latimeria ( 3 , figs 7.6A-B). In the juvenile/newborn specimen (PIMUZ T 3376), some tiny round teeth that are born on an ovoid surface, which may represent one or more basibranchial tooth plates (t.p.Bb?) (Fig. 3). It is also possible that the ovoid surface represents directly the basibranchial bones but the situation is unclear due to the preservation and the high compression of the bones. Therefore, the conditions relative to the basibranchial tooth plate cannot be determined (character 89 and 90).

Hyoid arch
In some specimens of Rieppelia (PIMUZ T 31, 1639 and T1755) is a large and rounded bone, often poorly preserved (Fig. S5g). This bone is very thin and shows lines of growth parallel to its external margin. The shape of this bone recalls the hyomandibula of Latimeria ( 10 , pl. XLIII).
In coelacanths, exemplified by Latimeria, the hyomandibula is cartilaginous but can be exceptionally partly ossified as in Laugia 3 . Therefore, the bone observed in Rieppelia may potentially represent an ossified hyoidmandibula.
An hourglass shaped bone with slightly rounded extremities is interpreted as the symplectic ( Fig. S5g-h). The bone is reminiscent to the symplectic of other coelacanth as for instance Latimeria ( 10 , pl. XLL; 3 , fig. 7.4). In coelacanths, the shape of the bone is also relatively constant and variates only in size.

Postcranial skeleton
The postcranial skeleton, comprising the axial skeleton, the basal support of the second dorsal fin and some bones of girdles and fins are preserved articulated in the holotype (PIMUZ T 5902) (Fig. 2a-b) and in some other specimens (PIMUZ T 3376 and 4985) (Fig. 3). It should be warned that due to the early ontogenic stage of the juvenile/newborn (PIMUZ T 3376) individual the girdles, except the pectoral girdle, were not ossified, which explain why they are not observed in this specimen. Furthermore, the small size of the specimen makes it difficult to distinguish the different bones of the axial skeleton and of the fin rays.
Of the available specimens, none show ossified lung plates, meaning that an ossified lung was likely absent in life (character 97).

Axial skeleton
The axial column of Rieppelia is very short with a total of 35 neural arches (n.a) (character 93) as counted on the holotype (PIMUZ T 5902) (Fig. 2). A similar maximal count is obtained for the neural arches in the juvenile/newborn specimen (PIMUZ T 3376). This low number of neural arches is one of the lowest known among coelacanths, identical to that of No long ossified ribs have been identified in any available specimens (character 96).
A count of 13 to 16 dorsal and 11 to 14 ventral radials (Ra) have been done in the holotype (PIMUZ T 5902) (Fig. 2a-b). The rods are symmetrical, flatten and large with proximal and distal expanded extremities. The first anterior dorsal and the two or three anterior ventral radials seem to support no fin rays.

Unpaired fins
The unpaired fins of Rieppelia include two dorsal fins, one anal fin and the caudal fin with a supplementary lobe (Fig. 2). The basal plate of the anal fin is not preserved in any available specimens. The anal fin (an.f) is distinctly a lobed fin, but is relatively small compared to the posterior dorsal fin (Fig. 2). The situation is similar to that of Foreyia, which has the anal fin smaller than the posterior dorsal

Pectoral girdle and fin
The pectoral girdle is composed of an anocleithrum, a cleithrum, an extracleithrum (character 91) and a clavicle, as in other coelacanths. The scapulocoracoid has not been observed. It is worth noting that in specimen PIMUZ T 1321, the bones of the pectoral girdle are very well preserved in 3D, being then not flattened (Fig. S4).
The anocleithrum (Ano) is simple (character 92) and slightly sinusoidal (Fig. 2). Its shape is very similar to the anocleithrum of Foreyia (the 'posterior wing of the prootic' of 1 ). The bone presents some digitations for the insertion of the muscle that presumably helps to elevate the posterior branchial arches 3 .
The cleithrum (Cl) is one of the most characteristic bone of Rieppelia, which is easily recognizable and often preserved in many specimens (e.g. PIMUZ T 1321, 1639, 1755, 3376 and 5902). It is a large boomerang-shaped bone (Fig. S4). The center of the bone is crossed by a strong lamina that delimitates an anterior and posterior portions of the cleithrum. The anterior portion is interpreted as a branchial lamina (br.l) (Fig. S4). It forms a broad medial extension that twists mesially along most the entire length of the cleithrum. The upper border of the lamina, which does not reach the dorsal tip of the cleithrum, is marked by an anterior rounded angle. This lamina is covered by the opercle, whose posterior margin accommodate the central lamina of the cleithrum. Therefore, a large part of the cleithrum is covered by the opercle unlike in most other coelacanths, but as in Foreyia that has, however, a thinner cleithrum. This lamina is very similar to the branchial laminae of the cleithrum of some lungfish, such as Eoctenodus 20 .
The posterior portion of the cleithrum is marked, in its posterorventral lateral surface, by digitation for the insertion of the extracleithrum.
The extracleithrum (Ecl) is always observed separated from the cleithrum. It is a bone a little less long than half of the cleithrum. Its distal and dorsal portion is thinner than its proximal portion contacting the clavicle.
The anterior tip of the clavicle (Cla), ovoid shaped, is remarkably smaller than the cleithrum (Fig. S4). From its anterior to its posterior portion, the clavicle twists medially and enlarges dorsally as a thin and large triangular bony portion that was overlapping the ventrolateral part of the cleithrum. The clavicle of Rieppelia recalls the clavicle of Megalocoelacanthus ( 13 , fig.   18c), except that in this latter the anterior tip is squarer.
The pectoral fin (pect.f) inserts behind the maximal curvature of the cleithrum (Fig. 2). This fin is distinctly large and composed of slender and elongated rays. The fin rays show an asymmetrical profile along the lobe with the longer fin rays located along the anterior leading edge. Compared to the pelvic and anal fins, the pectoral fin is large. There is between 37 and 44 rays in the pectoral fin (count based on PIMUZ T 1271 and 5902), which is the maximum number of rays observed in actinistians, together with Trachymetopon having 40 rays 21 . Foreyia has only 10 rays in the pectoral girdle, which is one of the lowest number of rays.

Pelvic girdle and fin
The pelvic bones (P.b) are remarkably small and thin proportionally to the rest of the skeleton (Fig. 2). The two paired bones are clearly separated (character 103). The pelvic fin (pelv.f) lies in abdominal position (character 102) (Fig. 2), as in the majority of actinistians. Although the length of the pelvic fin cannot be observed accurately, the lobe appears to be poorly developed (PIMUZ T 1271 and 5902), which is reminiscent to that of Foreyia 1 . The pelvic fin is then of the same size as the anal fin and is considerably smaller than the pectoral fin. The pelvic fin is composed of about 30 rays (count based on PIMUZ T 1271), all with small and sharp denticles.
This number of rays is in the upper range for coelacanths, and only Latimeria 3 and Trachymetopon 21 have more rays with 33 and 35 rays, respectively. The situation is then opposite to Foreyia that has only 12 rays in the pelvic fin, a low amount compared to other actinistians 1 .

Ornamentation and histology 2.9.1 Dermal bones
All of the dermal bones -except the gular plates, the oral margin of the premaxillae and the bones of the pectoral girdles -are heavily ornamented with numerous distinct rounded and pointed odontodes (character 28 and 54) (Figs 2a, S1a-b, S2, S3, S6a-b), an ornamentation similar to that of Foreyia 1 ).
The ornamentation of Rieppelia was shortly described by Ørvig 22 , and the histology of the dermal bone and the ornaments were thin sectioned and commented by Mutter & Heckert 23 .
Thin sections of dermal bones indicate that the ornaments are constituted of a cone of dentine set around a large pulp cavity and overlain by an external hypermineralised layer, representing therefore the typical odontode structure (Fig. S6c-e), a pattern already described by Ørvig 22 .
Scales and/or dermal bones having ornaments with the same structural organization is known in other coelacanths such as Miguashaia 24 , Undina 25,26 and Latimeria 12,27 .
The bony portion on which lies the odontodes is about 600 μm thick (Fig. S6c-e). Within this layer develops a network of vascular cavities and canals (vc) (Fig. S6c-e), indicating a high degree of vascularisation 23 . It should be noticed that this layer appears to be highly recrystallised and poorly preserved due to a strong compression of the bones during fossilisation.
Each odontode have a single proportionally and remarkably very large pulp cavity (pc) (Fig. S6c-e). It resembles to the large pulp cavity of the odontodes of Undina 25,26 or Latimeria 12 and is thus larger that the pulp cavity of the odontodes of Miguashaia 24 .
The dentine layer (de) forms the main body of the odontodes and is 200 and 250 μm thick ( Fig. S6c-e). From the pulp cavity develop many transversal dentinal tubules within the dentine, The external dentine layer is capped by a highly mineralized layer (en), which may possibly represent enamel (Fig. S6c-e). This layer is however very thin, 12 to 14 μm in thickness. The presence of enamel in Rieppelia is not surprising as the odontodes ornamenting the scales of, for instance Latimeria, Undina and Miguashaia are covered by a layer of enamel 12,24-26 .
On the dermal bones of Rieppelia, the odontodes show a variation of size according to their position on the dermal bones and to the generation to which they belong. Along the crest of the supraorbitals and the opercle (Fig. S4), where the bones angled, the odontodes appear to be slightly larger than those located elsewhere.
In PIMUZ T 1638 ( Fig. S6a-b), displaying a very well-preserved ornamentation, there is clearly two generations of odontodes, with small and low odontodes located between large and high odontodes. The presence of different generations of odontodes representing different stages of growth was already observed by Ørvig ( 22 , plate 2A). Superimposed odontodes is not obviously observed and most odontodes grow next to other odontodes (Fig. S6a). Few odontodes, however, appear to grow just above the marginal border of a neighbouring odontode (Fig. S6b). The situation in Rieppelia is thus definitively different from Miguashaia ( 24 , figs 3a and 4a) or Spermatodus ( 28 , fig. 1.3) that both have strongly superimposed generation of odontodes. As there is no obvious superimposed odontodes, it is unclear if there is a fixed number of generations of odontodes or if odontodes are growing constantly replacing either older or lost odontodes.

Scales
The holotype (PIMUZ T 5902) is the only specimen that has preserved the scales in situ on the body (Fig. 2a-b). The scales are subcircular to suboval ( 29 , fig 3) (Fig. S7a-b) as in Foreyia ( 1 , figs 2, S2) and Diplocercides and unlike Latimeria 24 , for instance. The scales show some variations of their ornamental pattern according to their position on the body.
The anterior portion of each scale is largely overlapped by the preceding scales. In this area, there are several concentric rings of growth. The exposed area is ornamented with numerous blunt spines and represents approximately one third of the area of the scale (Fig. S7a-c). There are about 25 blunt spines aligned on an anteroposterior axis and arranged in 5 to 6 rows, as already described by Rieppel 29 . The spines of the posterior most rows extend beyond the posterior margin of the scale. According to Rieppel 29 , the spines lack dentine. Unfortunately, no histological study was made to support this observation but his affirmation may be questioned because the histology of the dermal bones presents a highly mineralised layer, probably made of enamel. Indeed, it seems that the histological structure is similar between the dermal bones and the scales as exemplified by Miguashaia 24 and Latimeria 27 . Therefore, it would be surprising if the situation was not similar in Rieppelia.
Regarding the position of the scales on the body of the holotype (PIMUZ T 5902), the size of the spines appears to vary very slightly in size (Fig. S7c). On the upper part of the flank and anteriorly to the first dorsal fin, the spines are larger and longer than on the rest of the body. On the anal fin, the spines appear to be relatively small and short. Although the length of the spines varies from a scale to another, there is no variation of length of the spines within a single scale meaning they are not differentiated (character 112). Due to the preservation, it is hard to distinguish the condition of the openings for the lateral lines within the scales because of the preservation (character 110).
In the most ventral portion of the body (PIMUZ T 5902), there are some round to ovoid thick scales (Fig. 2a, not labelled and located below and around the possible basibranchial).
Those scales bear in their center between 10 to 15 small and low ornament with a round apex resembling to hemispherical bulges (Fig. S7d-e). The external rim of those scales is covered with many thin radiating ridges. When flipped in internal view, the scales display small depression in their center corresponding to bulges on the external aspect (PIMUZ T 5902).